Main-Sequence Lifetime Estimator

Estimate how long a star spends fusing hydrogen on the main sequence from t_MS ≈ 10¹⁰(M/M☉)⁻²·⁵ yr — since fuel scales roughly with mass while burn rate scales with luminosity — with a log-log mass-vs-lifetime chart against a naive 1/M comparison, and a log-scale bar chart comparing red-dwarf and massive-star lifetimes.

Main-sequence lifetime estimator

Fuel available scales roughly with mass, but the rate a star burns it scales with luminosity — and luminosity rises steeply with mass. So t_MS ∝ M/L, commonly approximated near Sun-like masses as t_MS ≈ 10¹⁰ (M/M☉)⁻²·⁵ yr. This is an order-of-magnitude estimate, not a stellar-evolution model — it departs most from reality at the very low- and very high-mass ends.

Mass (M☉)

Main-sequence lifetime

10 Gyr

t_MS ≈ 10 Gyr (1 × 10¹⁰ yr)

M ≈ 1 M☉G-type (Sun-like)

Actual (t ∝ M⁻²·⁵) — naive 1:1 fuel-to-burn-rate scaling (t ∝ 1/M). The gap between the two lines is luminosity's own steep rise with mass, doing double duty: more fuel, burned disproportionately faster.

Red dwarf (M) (0.2 M☉)

559 Gyr

Orange dwarf (K) (0.7 M☉)

24.39 Gyr

The Sun (G) (1 M☉)

10 Gyr

F-type (1.5 M☉)

3.63 Gyr

A-type (2.5 M☉)

1.01 Gyr

B-type (10 M☉)

31.62 Myr

O-type (40 M☉)

988.2 kyr

Bar length is on a log scale — the actual span between a red dwarf and a massive O-type star covers roughly six orders of magnitude, from far longer than the current age of the universe down to just a few million years.

A star’s mass decides almost everything about its life, and nowhere is that starker than in how long it lasts. A red dwarf a fifth the Sun’s mass will still be quietly fusing hydrogen long after the Sun has swelled into a red giant, shed its outer layers, and cooled to a white dwarf — while a star forty times heavier burns through its own much larger fuel supply so fast it’s gone in a few million years, a blink next to the Sun’s roughly ten-billion-year span.

The formula, and where it comes from

t_{\rm MS} \propto \frac{M}{L}

Available hydrogen fuel scales roughly with a star’s mass. If burn rate scaled with mass too, lifetime would barely change from star to star — but burn rate actually tracks luminosity, and luminosity rises steeply with mass (roughly L ∝ M^3.5 over much of the main sequence; see this site’s Stellar Mass-Luminosity Relation Calculator). Combine the two — more fuel, burned disproportionately faster — and lifetime falls off steeply with mass:

t_{\rm MS} \approx 10^{10}\left(\frac{M}{M_\odot}\right)^{-2.5}\ \text{yr}

The exponent -2.5 is exactly “1 (fuel) minus 3.5 (burn rate)” — it’s the mass-luminosity relation’s own exponent showing up here, not a separate fact about fuel. This calculator’s chart plots that actual scaling against a naive comparison line where lifetime falls off as just 1/M — as if burn rate scaled with mass alone — so you can see directly how much of the effect luminosity’s steepness accounts for.

Where this approximation holds, and where it doesn’t

This is an order-of-magnitude estimate, calibrated so a 1 M☉ star comes out close to the Sun’s own main-sequence span — not a stellar-evolution model:

It inherits the mass-luminosity relation’s own limits. That relation’s exponent isn’t really a constant 3.5 across the whole main sequence — shallower below about 0.43 M☉, closer to linear above about 20 M☉ — so a single -2.5 power law is least accurate at both ends.
The lowest-mass stars live even longer than this formula predicts. Red dwarfs below roughly 0.35 M☉ are fully convective, meaning they mix and burn essentially their entire hydrogen supply rather than just the core’s — stretching their already-enormous lifetimes further still.
Composition, mass loss, and rotation all shift real lifetimes. A star’s exact age when it leaves the main sequence depends on more than mass alone; treat this calculator’s output as “roughly this many years,” not a precise clock.
This describes the main-sequence phase only — the stretch spent fusing hydrogen in the core. It says nothing about how long a star spends afterward as a giant, nor about pre-main-sequence contraction before fusion ignites.

Reading the visuals

The log-log chart plots main-sequence lifetime against mass across the same range this site’s other stellar calculators use, with the actual t ∝ M^-2.5 scaling as a solid line against a dashed naive t ∝ 1/M comparison. Both fall as mass rises, but the actual line falls far more steeply — that gap between the lines is luminosity’s own disproportionate rise with mass, visualized directly.
The horizontal bar comparison puts a representative spread of stars — from a red dwarf up to a massive O-type star — side by side on a log scale, because the real span is too extreme for a linear one: a red dwarf’s estimated lifetime can run past the current age of the universe (~13.8 billion years) entirely, while a massive O-type star’s is measured in single-digit millions of years. No red dwarf has ever actually died of old age — the universe simply isn’t old enough yet.